Constant draw_state::preset::blend::INVERT

pub const INVERT: Blend = Blend{color:
          BlendChannel{equation: Equation::Sub,
                       source: Factor::ZeroPlus(BlendValue::ConstColor),
                       destination:
                           Factor::ZeroPlus(BlendValue::SourceColor),},
      alpha:
          BlendChannel{equation: Equation::Add,
                       source: Factor::Zero,
                       destination: Factor::One,},}

When combining two fragments, subtract the destination color from a constant color using the source color as weight. Has an invert effect with the constant color as base and source color controlling displacement from the base color. A white source color and a white value results in plain invert. The output alpha is same as destination alpha.